Continuous inductive train-control system for railroads



July 24, 1928.

E. H. LOFTIN CONTINUOUS INDUCTIVE TRAIN CONTROL SYSTEM FOR RAILROADS Filed Dec. 5, 1925 (Him Patented July 24, 1928.

UNITED STATES EDWARD 'H. LOFTIN, OF NEW YORK, N. Y., ASSIGNOR T0 GENERAL RAILWAY SIGNAIr PATENT OFFICE COMPANY, OF ROCHESTER, YORK.

CONTINUOUS INDUCTIVE TRAIN-CONTROL SYSTEM FOR'RAILRQADS.

' i Application filed December This invention relates to automatic train control and more particularly concerns a re ceiving and amplifying system for-train control systems of the continuous inductive type.

In train control systems of the well-known,

and voltages are induced in suitable car-carried receiving circuits located in inductive relation to the trackway conductors. As the alternating currents used in the trackway conductors are preferably small,the airgap through which the electrical induction must act necessarily large, and the voltages induced in the receiving circuits therefore compare:

tively small, it is necessary to provide suitable amplifying means for amplifying these terns by reason ofcommercial alternating voltages in order that the car-carried control apparatus may be operated in a reliable and satisfactory manner. V

In: the usual type of continuous inductive train control system, favorable traflic conditions ahead are usually indicated by the transmission of control currents or impulses from the track rails to the vehicle, while these currents are cut off under unfavorable trafiic conditions. It often occurs that alternating voltages are induced in the car-carried receiving apparatus of train control syscurrent power lines, or other sources of alternating current located in close proximity to the trackway. Undesirable alternating magnetic fields of'this nature may also result from the flow of large alternating propulsion currents in thetrack rails of electrified railway systems, the harmonics of the propulsion current being of the same order as the train control frequencies employed. These stray currents or magnetic fields frequently result in a false operation of the car-carried apparatus, causing a clear indication or operation of the car-carried devices under unfavorable traffic conditions, or some other 5, "1925. Serial No 73,403.

dangerous and undesirablefeffect. As these stray alternating currents have a different frequency from the current employed to transmit the train control impulses, it isdesirable and in fact essential to:the reliable operation of a train'control system of this type, that thereceiving and control devices be responsive to the train control frequency only. It is evident that the receiving equip ment must be very selective, as in the case of a railroad employing alternating propulsion currentsthe receiving equipment must re-' spond to the weak current of train control frequency while large currents of propulsion frequency are flowing in the track rails.

With the above and other considerations in mind, it is proposed in accordance with the present invention to provide receiving and control apparatus for automatic train control systems which'is sensitive to the weak induced voltages received from the trackway,

which is highly selective in that it responds to the train control frequency only, and

which is simple, compact and inexpensive as compared to the amplifying systems heretofore employed. More specifitally, it is proposed to provide an" amplifying system for train control employing a lightly loaded mechanically resonant relay together with means for making available the energy supplied by such relay. 1 f Other objects, advantages and 'characteristic features of the invention will become apparent as the description thereof progresses. i

In describing the invention in detail, reference will be made to the accompanying drawing in which a single' fi-gure has been shown, representing in a diagrammatic manner, a simple train control system of the continuous inductive type'provided with an amplifying system embodying the present invention.

The system of the present invention has been shown applied to a very simple continuous inductive train control system of the two-position 'type, it being understood that the receiving equipment is equally applicable to many other types of inductive train control.

The traclzway apparatus shown is of the fill ill)

type well-known in the art, and requires but ing normally energized .by current from the 7 track batteries 1 connected across the track rails at the exit end of each block Alternating train control current of a suitable frequency is applied tothe twotrack rails in series by the transformer 5 connectedrin series with the track battery 4 across "the track rails at the exit end of each block,the primary winding of this transformer being energized from the. transmission line 6 through he contacts 7 and 8 of the track relay 3 of the first block in advance. It is evident that the presence of a train in a given block, say the block J, shunts the track circuit and train control currents from the track rails behind the train in that block, causing the de energization of the track relay 3 at the entrance end of the block. The decnergization of this track relay 3 causes the train control current to be cut off from the track rails of the first block I in the rear of the occupied block by opening the energizing circuit for the transformer 0 at the confacts 7 and 8 of the relay 3 7 As wayside signals are sometimes used in connection with a train control system of this type, the wayside signals Z, which may be of the color light, semaphore or other suitable type, have been shown at the entrance end of each block. The well known circuits and devices for operating these way-- side signals have not been shown, as this apparatus is well. known to: those skilled in the art. and forms no part ofthe present invention. a r i ii railway vehicle has been conventionally representec in the block H by the wheels and axles 10. This vehicle isprovided with receiving coils 11 arranged in front of the leading axle of the vehicle and in inductive relation to the track rails 1. The receiving coils 11, which mayor may not be provided with laminatediron cores, are so connected that voltages induced therein by alternating currents flowing in opposite directions in the two trac r rails, will be additive.

The circuit through the'receiving coils is preferably tuned to resonance atthe train control frequency by means of the condenser 12, and is connected as shown in s'eries with the winding 13 of a tuned resonant relay R. The relay R may take any suitable form, and as shown comprises a laminated core 1 1 of general U-shape, having asuitable winding 13 on the back yoke thereof. A tongue or armature 15 is ri idly fixed to one leg of the core 14., and extends over the other leg to leave a small air gap in the magnetic circuit as shown, the armature 15 being preferably made of some flexible resilient material and being biased to the raised position as shown. Tl'ietongue 15 is so designed, constructed, and mounted,- as to have a periodicity or natural period of vibration equal to the frequency of the train control'curient. A vibrating reed or contact member 16 is soldered or otherwise suitablysecured to the tongue15 the reed 16 being designed to have the same natural period of vibration as the tongue. Thereed 16 is preferably mounted at some distance from the free end of the tongue 15, as with this arrangement the mechanical coupling betweenthe reed and the. tongue is loose, and. the two elements do not have much tendency to vibrate at two different frequencies as wouldbe the case if the reed 16 were mounted at the end of the tongue 15. An adjustable contact screw 17 is mounted in such a manner as to make a light contact with the reed 16 at the extreme end of the stroke of the reed when the relay is vibrated at the frequency to which it is mechanically tuned. This arrangement of the contact engagement insures that the load on the relay is very light and that the interference of the loading to the resonant tuning of the moving parts is a minimum.

the current carrying capacity of the contacts 16 and 17 of the relay R is necessarily limited, special apparatus must be provided to make this current available for controlling the car-ca-rried apparatus. In the present embodiment, this apparatus takes the formof a three-elementvacuum tube 18 of the well known type. The vacuum tube is provided with the usual filament 19;; grid 20 and plate 21, the usual filament heat-- ing battery 22 in series with a filament resistance 23 being provided as shown. The contacts 16 and 17 of the relay R are connected in serieswith the grid circuit of the tube 18 through a resistance unit 24, a portion of the plate battery 25 being included in this circuit, as shown. In order that the platecircuit of the-tube 18 may carry a minimum amount of current when the con tacts 16 and 17 are open, a suitable source of potential comprising the battery 29 is included in parallel with the grid circuit to place a negative potential bias on the grich a resistance unit 26 being placed in series with this battery to prevent an excessive flow of current through the contacts 16 and 17 when these contacts are closed. The output circuit of the vacuum tube 18 is connected to a suitable sensitive relay 27, responsive to unidirectional currents.

Any suitable form of train control appa ratus may be used to control the yehicle brakes, cab signalslor the ap'plicatmn oftems to give a restrictive control is usually accomplished bythe de-energization of an electro-magnetic device, the train control device TC has been shown, it being assumed that the de-energization of this dev ce acts In some suitable manner to 'glV a restrictive automatic control.

Operation.

In thedrawing, the system has been shown in its normal operating condition,'that is, with a trainproceeding under clear traffic conditionsahead with all circuits and devices properly energized. For convenience, the letters Band C have been used to designate the opposite poles of a suitable'source ofenergy, preferably a storage battery.

Considering first the operation of the system' of the present-invention under clear tratlic conditions, assume that a train equipped with the apparatus shown'istraveling ,in a clear block,- that is, with'no other train in the First two blocks in advance thereof. Under these conditions, alternating current of train control frequency flows in the track rails in advance of the train and induces.

corresponding voltages in the receiving coils 11. This voltage is impressed on the Winding 13 of the relay B through a circuit which is obvious from the drawings, and the tongue or armature 15'together with the reed. 16 are caused to vibrate at train control frequency, the reed l6 engaging the adjustable contact 17 at the extremity of each stroke. It should he noted that by reason of the electrical and mechanical tuning, voltages of other than traincontrol frequency do not cause the tongue 15 and-the reed 1G to vibrate at as great an amplitude as do the voltages of train control frequency, and for thisreason stray currents orniagnet-ic fields do not "effect the proper operatini of the car carried apparatus. V

The engagement of the reed 1 6 with the adjustable contact 17 impresses a positive voltage on the grid of the vacuum tube 18 through a. circuit which may be tracedas follows: from the filament 19, wires 80, 31 and 32, negative terminal of the plate battery 25, an intermediate positivepoint of the battery 25, through the wire 33, res1s't-- time unit 24, wire 3 stationary contact 17 reed 16 and armature 15 of the relay R, Wires 85 and 36 to the grid 20. Anegatii "e potential bias is maintained on' the grid 20 by the battery 29 through a circuit which is obvious from the drawings, thereby preventing the flow of any appreciable current in tl e plate circuit of the tube whenthe con- ,variation in grid potential insuresthat 1 tacts 16 and 17 are open. The resistance units 24 and 26 prevent the short circuit ofthe batteries and 29, when the contacts 16 and 17 areclosed, thus avoiding any undesirable arcing at the contacts which would cause these parts to pit and corrode "and would rapidly change of the relay R.

the mechanicaltuning The positive voltage impressed on the grid 20 causes the flow of an appreciably pulsating current in the plate circuit-,which current serves to energize the relay 27,;this relay having sufficient inertia, or being otherwise made slightly slow acting, through acircuit which may be traced as' follows: from the relay '27, wire 38, plate battery 25, wires 32, 31 and 30, filament 19 of the tube 18, plate 21 and wire-39 to the relay 27:. The energization of the relay 27 causes the energization of the train control device TC through a circuit which is'obviousifrom the drawings, and the train proceeds in the clear block without automatic restriction.

If the train under consideration enters a caution block, that is, the first block in the rear of an. occupied block, no train control current flows in'the track rails and the relay Ris not energized to close its contaets 1 6 and 17. Under these conditions, the grid 20 of the tube 18 is maintained at a negative potential wit-hrespect to the filament 19, and practically no current flows in the plate circult of the tube. The relay 27 is therefore deenergized, causing the de-energizat-ion of the train control device 'TC, and an automatic brake application or other restrictive control is imposed. I

As the train under consideration proceeds through the caution block and enters adanger or occupied block, the'train control current is shunted 110111 the track rails by the train in advance, and the relays R and 27 and the train control device TC remain de-energized. The train under consideration, therefore, continues under restrictive control in the-occupied block. I

From the description given, it is eviden that a highly selective and sensitive receiving system for automatic trainc'onti' ol sys tems has been devised. It should be particularly-noted that, due to the mechanical tuning of therelay R, t-he contacts 16 and 17 thereof ,areclos'ed only when a voltage of the proper frequency is induced in the receiving coils 11. It should also be observed that very appreciable pulsations in theplate circuit current of the tube 18 may be obtained, as the grid voltage'i nay be varied from a normal negativebias of say or 40 volts to a positive bias, whenthe contacts 16' and 17; are closed, of'iBO or 10 volts, thus providing a voltage variation of trre grid of from to volts. This larg IOU cient current flows in the plate circuit of the tube to energize the relay 27 under clear traiiic conditions.

Althou h the system of the present invention has "een described in a rather specific manner, and in connection with one specific form of train control system only, it should be clearly understood that the invention is capable Ofl certain modifications, changes and combinations and that. its scope 'is limited only as indicated by the appended claims..

WVhat it is desired to secure by Letters Patent, is

1. In an automatic train control system, a trackway means for carrying an alternating current of a predetermined frequency, a vehicle carried receiving circuit adapted to be excited by the field of said trackway alternating current, a relay in said receiving circuit having two vibratory elements, each of said elements having a mechanical periodicity equal to said predetermined frequency and one of said elements deriving its energy for vibration from the other, and train control means controlled by said vibratory elements. v

2. In an automatic train control system, trackway circuits energized by an alternating current of a predetermined frequency, a car-carried receiving circuit adapted to be energized by said alternating current, a relay connected in said receiving circuit and having a vibratory contact element mechanically tuned to resonance at said predetermined frequency, an amplifier having an input circuit and an output circuit, a source of energy, means whereby said vibratory contact of said relay connects said source of energy to said input circuit, and train control means controlled by said output circuit.

3. In an automatic train control system, in combination with trackway means for inductively transmitting alternating voltages of a predetermined frequency to a moving vehicle, car-carried apparatus comprising a receiving circuit, a relay in said receiving circuit, a vibratory armature on said relay having a mechanical periodicity equal to said predetermined frequency, a three-element vacuum tube having a grid circuit, means for normally fixing the potential of said grid circuit and means whereby the potential of said grid circuit is varied in accordance with the vibrations of said vibratory armature.

4:. In an automatic train control system, in combination with trackway means for in ductively transmitting alternating voltages of a predetermined frequency to a moving vehicle, car-carried apparatus comprising a receiving circuit, a relay in said receiving circuit having a vibratory armature mechanically tuned to resonate at said predetermined frequency, a three-element vacuum tube havinga grid circuit and a plate circuit, means for applying a source of potential to said grid circuit in accordance with the vibrations of said vibratory armature and an electro-responsive control device connected in said plate circuit.

5. In an automatic train control system, in combination with trackvvay means for inductively transmitting alternating voltages of a predetermined frequency to a moving vehicle, car-carried apparatus comprising a receiving circuit, a relay connected in said re ceiving circuit and having a vibratory armature, a vibratory contact reed secured to said armature, said reed and saidarmature being mechanically tuned to have aperiodicity equal to said predetermined frequency, a stationary contact arranged to be lightly engaged by said contact reed when said reed and said armature are vibrating at said predetermined frequency, a source of potential connected in series with said stationary contact and said contact reed, and a potential operated amplifying device having an input circuit connected with said source of potential and said contacts.

6. In an automatic train control system, in combination with trackway means for inductively transmitting alternating voltages of a predetermined frequency to a moving vehicle, car-carried apparatus comprising a receiving circuit electrically tuned to resonate at said predetermined frequency, a relay connected in said receiving circuit and having a vibratory armature, a vibratory contact reed secured to said armature, said reed and said armature having a vibratory periodicity equal to said predetermined frequency, an adjustable stationary contact arranged tobe lightly engaged by said contact reed at the extremity of each vibration thereof, a'three-element vacuum tube having a grid normally biased to a negative potential and a plate circuit responsive to variations of grid potential, and a source of potential controlled by the engagement of said reed and said stationary contact to apply a positive potential to said grid, and a train control device controlled by said plate circuit.

7. In an automatic train control system, in combination with trackway means for transmitting electrical impulses of a predetermined periodicity to a vehicle, vehicle'carried apparatus comprising a receiving circuit electrically tuned to resonate at said periodicity, an electro-mechanical device in said circuit having a plurality of movable parts each mechanically tuned to resonate at said predetermined frequency, an amplitier of the vacuum tube type having its input circuit controlled by said movable parts, and train control means controlled by said amplifying device. v 8. In an automatlc tram control system,

a traekway means for: carrying an alternating current of a predetermined frequency, a vehiclecarried receiving circuit adapted to be excited by the field of said trackway alternating current, a relay in said receiving circuit having two vibratory elements, each of said elements having a mechanical periodicity equal to said predetermined he.

quency and one of said elements being vibm torily superimposed at an intermediate point in the other, and vehicle control means controlled by said vibratory elements.

In testimony Whereofl afiix my signature.

EDWARD 3110mm" 

